Grappling heads mounted to booms serve a variety of mechanized functions. For example, the tree-cutting and delimbing device disclosed in applicant's co-pending application Ser. No. 08/189,644, now U.S. Pat. No. 5,441,090 discloses a boom-mounted head having a saw mounted thereto, adapted to cut trees and limbs, with the jaws of the head adapted to grapple tree trunks and limbs and loose brush. Another useful function of a grapple is to rotatably drive an auger and, after a hole is drilled, to manipulate and transport a pole for insertion within the hole. Other uses abound. Several features are desirable in a grapple to serve these various functions. The head must be highly maneuverable, and capable of being placed by the boom in virtually any position. It must be able to reach over, under or around obstructions. It should be continuously rotatable, in order to permit it to rotate an auger. The jaws of the head should be capable of evenly gripping either a regular or an irregularly-shaped object, and for this purpose the individual teeth that comprise the jaws should be independently-pivoted and driven by drive means adapted to supply an even force to all teeth regardless of their position.
A grappling head is typically are mounted to an articulated, or "knuckle", boom with the boom and head being driven by a hydraulic or other drive means. While knuckle booms and various types of grappling heads are well known in the art, prior such systems suffer from not having a full range of control in all planes, nor are the heads continuously rotatable.
Typically, the head in a boom-mounted device comprises a set of jaws adapted to grip an object, with the head having some degree of maneuverability. There may be provided as well a saw for cutting tree or brush. An example is shown in Canadian Patent 1,224,704 (Gaitten), wherein an articulated boom mounted to a truck is provided with a cutting head at its free end. The cutting head includes a set of jaws for gripping a tree limb or trunk, and a longitudinally-slidable circular saw. However, the Gaitten device does not include a boom having a sufficient degree of articulation to reach around or behind obstructions.
In order to achieve these objects, the head may be mounted on an articulated boom, with a linkage that permits the head to both pivot and rotate in much the same manner as a human arm and wrist permit the hand to be positioned in any orientation. Preferably, the head should be continuously rotatable relative to the boom; this requires the use of a rotary drive coupling to permit the hydraulic lines or other drive and control means driving the head to remain coupled with the boom without the lines twisting. Preferably, at least one of the segments of the boom should be extensible. As well, one of the joints of the boom may be provided with means to pivot by a full, or nearly full, 360 degrees; this permits an operator to extend the head underneath obstructions, such as power lines, and bring the head upwardly and rearwardly around the obstruction.
These and other objects are addressed by the present invention.